There is substantial literature in the art with respect to the hydrogenation of aromatic amines, e.g., methylenedianiline to produce 4,4'-methylenedi(cyclohexylamine), also called bis(para-aminocyclohexyl)methane, and bis(4-aminocyclohexyl)methane hereinto after referred to as PACM.
Some of the early hydrogenation work to produce PACM was done by Whitman and Barkdoll. et al. and their work is set forth in a series of U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; and 2,606,928. Basically the processes described in these patents involve the hydrogenation of methylenedianiline at pressures in excess of 200 psig, preferably in excess of 1,000 psig. at temperatures within a range of 80.degree. to 275.degree. C. utilizing a ruthenium catalyst for the hydrogenation. The hydrogenation is carried out under liquid phase conditions and an inert organic solvent is used in the hydrogenation process. Examples of ruthenium catalysts utilized for the hydrogenation process include ruthenium oxides such as ruthenium sesquioxide and ruthenium dioxide; and ruthenium salt.
Brake, et al. continued in the development of processes for manufacturing PACM by hydrogenating methylenedianiline. They found that if the ruthenium was carried upon a support and the support was alkali-moderated, the catalyst was much more active and catalytically effective in producing the desired hydrogenated PACM product. Alkali moderation was effected by contacting the catalyst and support with alkali metal hydroxide or an alkoxide; also, such alkali moderation of the catalyst could be effected prior to hydrogenation or in situ during the hydrogenation. Representative patents showing the utilization of alkali moderated ruthenium catalysts to hydrogenate methylenedianiline include U.S. Pat. Nos. 3,636,108; 3,644,522; and 3,697,449. Alkali metal and alkaline earth metal nitrates and sulfates have similarly been shown effective in U.S. Pat. No. 4,448,995 under high pressure (4000 psi) hydrogenation conditions. Representative supports in the '449 patent include bauxite, periclase, zirconia, titania, diatomaceous earth, etc.
U.S. Pat. No. 3,959,374 discloses a process for the preparation of PACM by pretreating a mixed methylenedianiline system with a nickel containing hydrogenation catalyst prior to hydrogenation with ruthenium. The pretreatment was alleged to overcome low yields (52.4%) and long reaction associated with nickel and cobalt. Ruthenium catalysts, although commonly used for hydrogenation, were not suited for hydrogenation of a feed containing impurities, e.g., isomeric impurities. Impurities in the feed allegedly caused a rapid decline in activity and hydrogenation efficiency.
U.S. Pat. Nos. 3,347,917; 3,711,550; 3,679,746; 3,155,724; 3,766,272 and British Patent No. 1,122,609 disclose various isomerization processes and hydrogenation processes to produce PACM containing high trans,trans-isomer content; i.e. an isomer content near equilibrium typically 50% trans,trans-, 43% cis,trans and 7% cis,cis-. As in the early work ruthenium catalysts were used to effect isomerization. This product was often called PACM-50.
Allen in U.S. Pat. Nos. 4,394,522 and 4,394,523 discloses processes for producing PACM by carrying out the hydrogenation of MDA in the presence of unsupported ruthenium dioxide at pressures of at least 2500 psia or in the presence of ruthenium on alumina under pressures of at least 500 psia and preferably from 1500 to 4000 psia in the presence of an aliphatic alcohol and ammonia.
Other catalysts have been utilized for the hydrogenation of methylenedianiline and examples are shown in U.S. Pat. Nos. 3,591,635 and 3,856,862. Both disclose the use of a rhodium component as a catalytic material and each require the use of an aliphatic alcohol as a solvent. The rhodium is alkali moderated using ammonium hydroxide as a pretreatment or by carrying out the reaction in the presence of ammonia. European application No. 66.212 discloses the use of rhodium on alumina to obtain 15-40% trans,transisomer ratio but again the pressures are high (4000 psi).